Whenever I install a standalone SQL instance (installing on a failover cluster adds a few more steps) on a x64 host (who would install SQL on a x86 in 2012?), I always do the following:
I install the latest version of Red Gate SQLBackup.
I affect Microsoft prescribed best practices for TEMPDB optimal concurrency. As part of this I add the 1118 trace flag to the startup parameters of the SQL service.
I install Ola's SQL maintenance process.
I install Adam Machanic's peerless sp_WhoIsActive.
I add the instance to my Ignite monitoring.
I add the host and instance to my implementation of Muthasamy Kumar and Yan Pan's wonderful SQL_Inventory PoSH process.
How about you? What steps do you like to take when you install SQL on a new machine?